500mb apparently used in 30 miniutes?!

Bought R49 airtime at 19:00, SMS received stating R57 airtime balance. Bought 500mb for R49, I assume now that I have 500mb's and R8 airtime. However, an hour later my messages are not coming through. According to my phone I don't have any data or airtime ?? Called the call centre and they say I used it. Stating my data was used up because I have an iPhone? It had this phone for a year and know how it works. 500mb's of data in 30 minutes has never happened. If I used it by downloading something / streaming I would understand. Browsing a neotel website and whatsapping has never used up 500mb's of anyone's data in 30 minutes. They say I used it and that's that. I feel ******. If I used the data I would not be sitting on the phone discussing it. This is day light *******